Color gamut refers to the range of colors that can be output by a device, and color space refers to the color model used to represent colors that can be output by the device. For example, the color gamut of a display device refers to the range of colors that can be displayed by the display. Display devices commonly employ the red-green-blue (RGB) color space, in which each color is represented as a combination of a red color component, a green color component, and a blue color component.
The colors that can be output by a device having a particular color space is equal to 2n×m, where m is the number of color components, or channels, of the color space, and n is the number of bits used to represent the value of each channel. For example, for a display device using the RGB color space in which each color component has 8 bits, the value of each color component can be any one of 28=256 different values, such that 2563=16,777,216 different true colors can be represented.
To increase, or extend, the color gamut for a particular color space, or to increase the accuracy to represent color values, the number of bits, or the bit depth, of each color channel is typically increased. However, increasing the bit depth of a color space's channels significantly increases memory or storage space requirements. For example, an 8-bit per-channel RGB color space image file uses 24 bits to represent a pixel, whereas a 12-bit per-channel RGB color space image file uses 36 bits to represent a pixel. Increasing the bit depth of an RGB color space from 8 bits to 12 bits thus results in a 50% increase in the amount of memory or storage space needed.